Pesky Weeds

On the second of our three educational courses we looked at problem weeds, and how to identify, control and dispose of them in line with our processes. The talk was given by Carol Seery (Wirral Environmental Trust Trustee). Carol holds a RHS Master of Horticulture qualification.

It is hoped that by running this course that our volunteers and staff will be able to educate the people we support in the effective removal of common weeds found here on the farm.

Perhaps one of the most important things to determine, is whether a plant is an annual or a perennial. Perennials often regenerate from broken roots, so if the root system is broken up into pieces and left in the soil during the weeding process, this can make the weed problem worse than it was before. Another key point to prevent the spreading of weeds, is to remove them before they can set seed (before they flower). Seed (especially perennial seed) may survive our composting process, so it is important that we do not compost seed.

Definition of a weed – ‘a plant in the wrong place’.

This Gardener’s World video shows some differences between annual and perennial weeds and how to get rid of them.

Dale Farm is certified by the Soil Association and as such we cannot use any pesticides, insecticides or herbicides. Because we are limited in the way we can get rid of weeds, it s important to identify different types of weed, how they spread and the most effective way to remove and dispose of them.

Although many weeds are good for wildlife, they compete with our crops, so should be discouraged from creeping onto growing areas.

The control of weeds by ‘no dig gardening’, will be discussed by Carol Seery in our next talk. Please see our future ‘ no dig gardening’ blog. ‘No dig gardening’ and the use of thick organic mulches over cut weeds has been discussed within this blog below.

We recognise the importance of many weeds for wildlife and so we try only to restrict these within our boundaries that will impact on yields of our products.

Farm disposal methods

There are two main ways to deal with weeds and compostable material here at Dale Farm.

Recycle bins can be used for:

• The upper stems from vegetables, i.e. peas, beans, tomato, squash, etc. but not potato.
• Any unused / rotten vegetables (not potato), any kitchen waste such as peeling, etc.
• Do not dispose of meat, fish, or carbohydrate such as bread and rice because this attracts vermin.
• Grass cuttings (but not if it has gone to seed).
• Annual weeds that haven’t gone to seed. Although the composting temperatures are usually high enough to destroy the seeds of annual weeds, it is better to dispose of all seed in the same way and put them in the weed bins.
• Anything that will compost completely and will not cause a problem when spread on the field.
• Never put perennial weeds on the compost heap (especially their seeds or roots). If you don’t know if a weed is an annual or perennial please put it in the weed bin.

Weed bins can be used for:

• Any type of perennial weeds.
• There are too many weeds to list here but, if you are unsure, then it goes in the weed bin.
• We want to try and burn all woody weeds, such as: brambles, ferns etc. We will also try to burn the roots of perennial weeds (if not covered in soil).

Herb bennet (Wood avens (Geum urbanum))

Perennial with rosettes of leaves made up of three to five rounded lobes. Yellow five-petalled flowers held above to 60cm. Spreads by root fragments and seed. Underground, herb bennet grows from a short, horizontal rhizome and produces a tangle of wiry roots. Herb bennet self-seeds, and its hooked seeds are easily distributed on clothing and animal fur, it can quickly spread. This plant spreads as a rhizome and can regenerate from small pieces of root and so it is important that the roots are properly removed to avoid unnecessary spread. The good news is that hand removal of this plant is reasonably effective. Another method of removal is to chop down the plants and smother it with a thick organic mulch or by using cardboard to drown out the light.

Couch Grass (Elymus repens)

This is a very common weed on the farm. The roots are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. Seed can easily be spread. The rhizomes tend to grow in straight lines away from the parent plant.  However, as couch grass is capable of outcompeting, entangling and smothering smaller or less vigorous plants, it is a good idea to remove it from veg beds. couch grass can regenerate from rhizome fragments, so avoid chopping them up by hoeing or chopping them. If the soil is as yet uncultivated, a good way to get rid of these weeds is to smoother out the light with an organic mulch or cardboard.

Bindweed (convolvulus)

This is another common weed that comes in from the surrounding woods. It is a twinning perennial climber and once established is difficult to get rid off. It is regularly seen creeping in from the Heswall Dales. Convolvulus produces white trumpet flowers in summer. Fleshy cream roots run deep and can regrow from small sections. There are two types: hedge bindweed and field bindweed. The most familiar and problematic bindweed is hedge bindweed, which is fast-growing with slender, twining stems and large white trumpet flowers. Bindweed is long-lived and hard to get rid of, especially when it’s growing amongst plants, because the fast-growing root system grows right through the roots of other plants. In beds and borders, digging out bindweed roots is the only way to tackle this problematic weed. Winter to early spring is a good time to get on top of it, before plants start growing. Every piece of root left in the soil will grow into a new plant, so remove every last bit wherever possible. Use a fork to avoid breaking up the root. In summer, if it’s not possible to dig up roots, then cut or pull off shoots to weaken growth. If you can wait 12-18 months before planting, the easiest way to kill all perennial weeds is to cover the soil with something that excludes all light. Plants need light in order to make food, so in the dark, even the toughest weeds will succumb in time.

Ground Elder (Aegopodium podagraria)

Ground elder can regenerate from small sections of rhizome (underground stems able to produce roots and shoots). New plants or soil containing fragments of rhizome can unintentionally bring ground elder into the farm. Once introduced to soil, ground elder roots spread quickly. Composting roots or chopping them up when digging might also unwittingly spread it. The best ways to get rid of it are: chop it down and spread areas with a thick mulch/cardboard, dig out established plants, get rid of seedlings early in the season or, cut back established plants as they try to grow.

Bramble (includes blackberry, European blackberry, black heg, wild blackberry etc.)

The bramble or, as many of us know it, ‘blackberry’, is a thorny, fruiting shrub of the rose family, famous for its dark berries, which are relished by people and animals alike. It grows well in a variety of habitats, including woodlands, hedgerows, gardens, scrubland, cliffs, roadside verges and waste ground. Its dense bushes provide valuable protection for nesting birds and good habitat for a range of other small animals. Be sure to check for nesting birds or other animals before cutting back. Bird nesting is between March and the end of August. It is a good idea to control the spread of any bramble plants, to stop them growing into cultivated areas where they could smother other plants or become a hazard.  Blackberries can be propagated through leafy stem cuttings as well as root cuttings, so be sure to remove all pruned plant from the area as well as their roots. The best ways to get rid of established brambles is too: dig them out, keep them in check by pruning back, or chop them down and mulch with a very thick layer of mulch. Seedlings are much easier to get rid of, so remove as soon as they appear.

Dandelion (Taraxacum officinale)

If you are ever tempted to blow the seed heads, don’t! This weed is easily spread and is a common feature at the farm. Although a valuable wild flower, it is not a plant that we want on the farm’s growing areas. Dandelions have a very long tap root, that must be fully removed to stop the spread of this plant. The best ways to prevent dandelions spreading is not to allow it to go to seed. Ensure that the seeds, plant and roots (without soil), are put in the weed bin. For larger areas, it might be easier to remove the foliage and smother with a heavy mulch. If you are brave enough to dig them out, you need to ensure that you remove the whole tap root.

Dock (Rumex obtusifolius)

Another of the farms pesky weeks, these plants have a long tap root and if any is left behind, new plants will spring up from the fragments. Docks spread easily and the seed can remain viable for many years, so it is important that seed heads are burnt. There are several ways to help get rid of these pesky weeds: Smother them with mulch, hoe out the seedlings, remove seed heads and dispose of the plant, root and seed on the weed bin (ensure you get all the root). If you have a few of these plants, you might consider chopping down the foliage and cover with cardboard or a thick layer of organic mulch to exclude light to both the foliage and roots.

Fern (Bracken is a generic term that is used to describe many varieties of Fern that grow in the UK)

This tends to sneak in from around the surrounding woods. If left unchecked, bracken can form dense colonies that prevent the growth of other plants (including natives). It regularly pops up in the poly tunnels. Ferns can cause unwelcome competition for our plants, so it is important to control their spread onto the farm. Bracken is quite an invasive plant, able to spread into by spores blown on the wind and by rhizomes which spread from the nearby Heswall Dales.

Remove young plants that grow far from existing clumps of bracken (and have likely grown from spores), this will prevent them establishing. Use a border fork to lift mature plants, making sure to insert deep enough to get as much of the rhizome out as possible. Repeated removal of new stems and sections of rhizome will weaken and eventually eradicate bracken. Again, another method of removal is to chop down the plants and ensure the area covering the plants and roots are covered with a thick mulch to eradicate light.

Horsetail weed (common horsetail – Equisetum arvense)

A nightmare weed that has become a persistent problem in the fruit area of the farm. This weed should not be allowed to spread or proliferate! Horsetail is a very successful plant, able to spread by spores and rhizomes. The early shoots in spring produce spores that are dispersed long distances by the wind, but the spores are short-lived and need damp conditions to germinate and grow. Horsetail is more likely to spread by rhizomes, as these can grow in a range of conditions. 

Digging it out can be very difficult, since the roots can go down a long way – 2.4-3m (8-10ft) and even more. But it’s always worth starting by digging out as much of the roots as possible. Be rigorous as even small pieces left in the ground can re-grow into a new plant. A fork and hand fork are usually better tools than a spade and trowel, which will cut the roots into smaller pieces. Once you have removed most of the horsetail, covering the soil with weed-control membrane (landscape fabric) or even thick black polythene will exclude light and may starve the roots, so they die. This can take many years until the horsetail is completely exhausted and eradicated.

To add insult to injury horsetail is thought to be allelopathic. Allelopathy has been defined as a common biological phenomenon by which one organism produces biochemicals that influence the growth, survival, development, and reproduction of plants around it.”

Common Stinging nettle

Although their sting is not dangerous, it is unpleasant. It is herbaceous perennial with creeping horizontal stems and spreading roots that survive through winter and produce new growth each spring.  Pendulous catkin-like flowers are produced from late spring to early autumn. Stinging nettle plants can grow to 6ft, but there are smaller annual plants that only grow to approx. 60cm. They can regenerate from sections of rhizome or stolon, they may be spread unintentionally by chopping them up when digging.  Small stinging nettles are annual, so they release large amounts of seed to ensure success. The good news is that you can easily control the spread of stinging nettles by deadheading and removing their seedlings. Use a strimmer, brush cutter or mower to control large areas of common stinging nettles. Cutting back new growth regularly will weaken and eventually kill plants, you can further reduce their growth at this point by covering in a thick organic mulch. Young plants can be hoed out, but be careful not to leave any root.

Creeping buttercup (Ranunculus repens)

Creeping buttercup is capable of outcompeting and smothering smaller or less vigorous plants. It is easily recognisable by its glossy yellow flowers. It can grow practically anywhere, but particularly likes poorly drained soil. It produces flowers from April to August, much of the ripe seed lands near the parent plant, although wind and birds can transport seed further. In damp soils, creeping buttercup grows strongly and quickly, spreading by *runners that produce roots and shoots along their length. This makes it a tricky weed to eliminate from the garden, as it’s difficult to remove the whole plant from the ground. It’s best to get rid of it when it’s young, before it’s had time to spread. Plants can be killed by cutting back the growth and mulching with a thick layer of organic material. Where it is widespread, it maybe easier to carefully clear the whole bed or area of it, by cutting back the plants and mulching the ground. the creeping buttercup is a regular weed at the farm and a difficult one to get rid of.

*Runners are different to rhizomes, a runner grows along the ground, a rhizome grows underground. Runners produce new clone plants at nodes along the stem, while rhizomes can give rise to new shoots from buds. Runners do not store starch, while rhizomes can store starch to help the plant survive. Runners produce new plants that are genetically identical, while rhizomes can produce new plants that show genetic variability.

Willowherbs (Roseby, Great, Broadleaved, Pale, American, and Hoary are amongst the most common in the UK)

Some are native to the UK and some have been introduced, they are all perennials. As a rough outline, they all start the same way in spring with low rosettes of of leaves and grow to various heights from 75cm to 2m. They all have pink flowers and eventually produce woody stems. They all produce spikes of purplish – pink flowers. Generally they reproduce from rhizomes spread from the roots or from seed. Seeds appear in summer and autumn, so it is important to remove them before they reach this stage. Fortunately they have shallow roots and can easily be pulled out,

Annual weeds

Annual weeds are prolific, but the good news is that they are often easier to remove and destroy than perennial weeds. Annual weeds have very simple and shallow root systems, so simply hoeing the tops off or pulling the weeds up will be enough to control them. The roots simply don’t have the ability to gather enough energy to re-grow from scratch.

It is important to remove the flowers before they set seed, annual seeds are generally easier to ‘destroy’ than perennial seeds at the temperatures generated in the compost bin. But…… to ensure that we do not get unwanted weeds, all flowers and seed heads are to be disposed of in the weed bin, the plants and roots can go in the recycle bin. If you are at all unsure whether a weed is a perennial or an annual, please put them in the weed bin.

These weeds rely on spreading by producing lots of seed, and germinating and producing new plants quickly. The most effective way to stop annual weeds spreading is to remove them before they have the chance to set seed. Unlike perennial weeds they do not generally regenerate from rhizomes or roots left behind after weeding.

Identification of Annual Weeds

Chickweed (stellaria media)

Chickweed is most easily identified by its small white star-shaped flowers and tiny white line of weaved hair that grows along the stem. You can expect the Stellaria media to vary in size between 5cm and 50cm with oval-shaped leaves that have pointed tips. The texture of the leaves can vary from smooth to slightly hairy. Chickweed is easy to pull and hoe out, however, chickweed seeds easily spread.

Groundsel (Senecio vulgaris)

A common weed that is easily spread by seed, but the good news is that it is easy to pull out. The stems branch out into little clusters which have small yellow flower heads. The leaves of the Senecio vulgaris are evenly spaced on the stem and have toothed edges. Propagates by seed, produced prolifically through the year. In optimum conditions, life cycle can be very short, from seed to seed in under six weeks.

Hairy Bittercress (Cardamine hirsuta)

This little weed gets everywhere, but an easy one to remove. Whilst it only grows to a few centimetres high, this little rascal has a hidden talent. The seed pods formed after flowering can explode and disperse the seeds several feet away, so make sure you identify and control this weed well before its flowers set to seed. It is very good at spreading on loose ground where there is gravel or on pathways, it has shallow roots, but be warned, if this one gets a grip, you will be weeding it out for years to come.

Annual Meadow grass (Poa annua)

Cut firmly and diagonally into the roots. Because Annual Meadow Grass has no underground stems, once its roots have been removed the plant will die (provided all roots have been removed). Annual meadow grass, Poa annua, can be found growing all year round, carrying out its short, six-week cycle of germinating, flowering and setting seed. This being the case, it can appear in large clumps, getting in the way of other plants. Although this can be easily confused with the perennial couch grass, but unlike couch grass, this weeds does not spread by rhizomes.

Yellow oxalis/creeping woodsorrel (Oxalis corniculata)

Many species of oxalis are highly valued as garden or houseplants, but there are some that grow and spread very quickly and become a problem. The leaves look at little like clover. There is a tendency for oxalis to proliferate in the polytunnels at the farm. With the stems being able to root where they touch, it doesn’t take this ground invader long to cover a fair-sized area, along with the addition of producing a vast quantity of seed which is thrown out of their seed pods to ensure an even wider spread. These weeds need to be properly dug out and removed before they go to seed.

Cleavers (sticky weed (Galium aparine))

Cleavers produces bright green, climbing or sprawling stems up to 1m (3¼ft) long. The plant has whorls of slender green leaves and clusters of tiny, white, four-petalled flowers from May to August.  Tiny, white flowers are followed by small, spherical, green fruit sometimes flushed purple. Leaves, stems and seeds are covered in stiff, hooked hairs, so they can easily be carried on clothes or animal fur. They produce large amounts of seed and if allowed to establish can suffocate nearby plants. Cleavers is often not noticed until it is large enough to be scrambling into other plants or sprawling out into a bed, at which point it will likely already have set seed – so a single plant can quickly become a patch of cleavers seedlings.  The easiest way to get rid of it is to hoe it, pull it out or smother in an organic mulch.